Since 1987 the Upper Peninsula Power Company (UPPCO) has been experiencing a large number of lightning arrester failures, on a portion of their distribution system in southern Marquette County, Michigan. It was in the area of the US Navy's Extremely Low Frequency (ELF) antenna where the distribution system had been recently reconfigured so that the transformers were connected line-to-line in order to eliminate interference from the antenna. A study was done which determined that the system was susceptible to ferroresonance during single line faults under highly loaded conditions and that the overvoltages experienced could be causing the lightning arrester failures. This conclusion was further strengthened by a statistical study which compared the actual number of failures to an expected number of failures given the system's loading condition and fault rate.
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